Re: [R] Create a data frame of all possible unique combinations of factors

[David Winsemius]

On Jul 5, 2011, at 7:16 PM, Q wrote:
Hello,

I'm trying to create a data frame where each row has a unique  
combination of
factors.
I start with a vector of species like so:

1> test <- c("A","B","C","D")
1> test
[1] "A" "B" "C" "D"

To get all species combinations I have used expand.grid like this:

1> pairs <- expand.grid(test,test)

1> pairs

  Var1 Var2

1     A    A
2     B    A
3     C    A
4     D    A
5     A    B


snipped
Now I want to select only the unique pairs, which I have tried to do  
with
the function "unique":



1> unique(pairs)

 You want the duplicated function or more precisely its negation, ...  
and you need to sort within rows if yoy want (b,a) to look like (a,b).



, but that doesn't do anything... I guess because it considers A,B  
to be
different from B,A.  The data frame I would like to end up with  
should look
like this.

> pairs[!duplicated(t(apply(pairs, 1, sort))), ]
   Var1 Var2
1     A    A
2     B    A
3     C    A
4     D    A
6     B    B
7     C    B
8     D    B
11    C    C
12    D    C
16    D    D

The t( ) is needed to get the row-wise arrangement restore after apply  
transposed it.

        [[alternative HTML version deleted]]
Nabble allows posting in plain text. You should.


PLease --->
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html

--

David Winsemius, MD
West Hartford, CT

______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.